This invention relates generally to cannulas adapted for both oral and nasal applications for monitoring breathing of a patient, sampling the end tidal CO2 content in the exhaled breath of a patient to determine the patient's CO2 blood concentration level, or supplying a treating gas, such as oxygen, to a patient. In addition, the invention relates to a method of manufacturing a cannula adapted to communicate with both nasal passages and the mouth of a patient for use in monitoring breathing, sampling end tidal CO2, supplying a treating gas and is also suitable for the detection of apnea (the absence of breathing).
Nasal cannulas are commonly used to administer a treating gas, such as oxygen, to humans having respiratory problems. Illustrations of nasal cannulas used for this purpose are found in U.S. Pat. No. 3,802,431, for example. Nasal cannulas have also been used for inhalation therapy, made possible by development of inhalation sensors, such as described in U.S. Pat. No. 4,745,925, for example. A nasal cannula can be used to monitor breathing and for detection of apnea when connected to an inhalation sensor.
Nasal cannulas additionally adapted to communicate with the mouth of a patient to permit administration of a gas or sensing of apnea during periods of mouth breathing or nasal blockage are also known.
The present invention relates to a novel cannula and method of manufacturing the novel cannula having the ability to communicate with both nasal cavities as well as the mouth or oral cavity of a patient. This apparatus and method provides, in the preferred embodiment, disconnectable mandrel components which, when assembled with one another, form a mold assembly over which a cannula forming polymeric material is applied, and which, through the capability of each mandrel component being disconnectable from the other mandrel component(s), facilitates removal of the mandrel components from the formed or manufactured cannula.
Prior art relating to dipping of a part in a plastisol to create a coating is exemplified by U.S. Pat. Nos. 3,906,071, 4,695,241 and 4,800,116, and the disclosures of those references are hereby incorporated by reference.
The closest known prior art is believed to be a sampling cannula sold under the Salter Labs “One—No. 4001 oral/nasal CO2 sample line” trade designation. This cannula has a pair of prongs or sampling line(s) which each communicate with one nostril of the patient and a pair of straight prongs or sampling line(s) which both communicate with the oral or mouth cavity of the patient. A U-shaped wired is glued or otherwise affixed to the exterior surface of the main body of the cannula but the wire extends only about half the length of each of the oral or mouth cavity prongs or sampling line(s) and along the facepiece of the cannula. The wire does not extend along the nares. All of the nasal and the oral prongs or sampling line(s) communicate with an internal passage and thus communicate with one another so that the cannula can only perform one function. The leading free end of the oral or mouth prongs or sampling line(s) can be bent over in front of the teeth of the patient and any excess length of the prong(s) or sampling line(s) can be trimmed, as necessary. This cannula, of Salter Labs, is formed by a cannula mandrel assembly comprising a pair of mouthpiece/nasal mandrels and a facepiece mandrel with an intermediate section of the facepiece mandrel having a pair of spaced apart through holes for each receiving a leading end of one of the mouthpiece/nasal mandrels. Each mouthpiece/nasal mandrel has a first straight section which forms a straight molded mouthpiece and a second straight section which forms a molded nare. A bend is formed in each mouthpiece/nasal mandrel, between the first and second straight sections, to prevent further sliding movement of the facepiece mandrel along the pair of mouthpiece/nasal mandrels.